The present invention is related to a video coding apparatus and a method thereof for coding a digital compressed video signal having a compression format to obtain a digital coded video signal having the same, or different compression format. More specifically, the present invention is directed to such a video coding apparatus and a video coding method, capable of coding the digital compressed video signal by utilizing information about the compression of this digital compressed video signal.
Recently, digital video signals are widely used in various technical fields, since technical aspects of digital data related to data transfer techniques, data storage techniques, and data process techniques have been developed. Most of these digital video signals are usually compressed so as to reduce coding amounts thereof. There are plural compression formats. However, there is no united compression format. Also, most of these plural compression formats do not own compatibility among these compression formats. As a consequence, there are many difficult cases that a video (picture) which has been compressed by a certain compression format cannot be directly used in a system with employment of another different compression format. Otherwise, even when the same compression format is employed in two systems, there are large differences in coding amounts per unit time (bit rates) between these two systems, since these two systems own different limitations in data transfers and data storage capacitances. Similarly, there are possibilities that a video which has been compressed in one bit rate cannot be utilized in a system which introduces the other bit rate.
Under such a circumstance, various compression format conversion techniques have been researched/developed by which digital video signals compressed in one compression format are converted into digital video signals compressed in another compression format. These conventional compression format converting techniques are known from, for instance, Japanese Laid-open Patent Application No. Hei-10-271494 opened in 1998. This opened conventional technique describes the method for converting the bit streams of the moving pictures having the spatial resolution different from each other. In this bit stream converting method, the moving picture which has been compressed in the MPEG-2 format and owns the high resolution is inputted, whereas the moving picture compressed in the H.263-recommended compression format and owns the low resolution. Then, this conventional converting technique is featured by that since the motion vector of the MPEG-2 formatted bit stream as the input video data is corrected, the corrected motion vector can be utilized as the motion vector of the H.263-formatted bit stream as the output video data.
However, the above-described prior art owns the following problems:
(1). Since the motion vector of the input stream (input bit stream) is utilized irrespective of the magnitude of the motion prediction error caused by the motion vector of the input stream, there are some cases that the input stream is coded based upon such a motion vector having a large motion prediction error. In this case, there is such a possibility that this coding operation may cause a larger prediction error to be produced, resulting in deterioration of image qualities.
(2). Since all of the actual images are decoded and then are re-coded, the errors may be produced in the decoding stage and also the re-coding stage. There is another possibility that these errors may cause the image quality to be deteriorated.
(3). Furthermore, a large number of calculation amount is necessarily required so as to execute the decoding process operation and the re-coding process operation.
The present invention has been made to solve the above-explained problems, and therefore, has an object to achieve the following aspects:
(1). When a motion vector of an input stream (input bit stream) is reused, deterioration in an image quality is reduced, which is caused by reusing such a motion vector having a large motion prediction error.
(2). Both a decoding operation for an input stream and a re-coding operation for an output stream are deleted, so that deterioration in image qualities which is caused in these process steps is reduced.
(3). Also, a calculation amount required in compression format converting operation is reduced.
Moreover, the present invention owns another object to shorten a process delay required in the compression format converting operation, as compared with that of the conventional compression format converting operation.
To achieve the above-described objects, a video coding method, according to the present invention, is featured such a video coding method for performing either a partial stage of all stages of a decoding process operation with respect of an input stream and for coding the decoded digital moving picture by way of the same, or different compression format as/from the compression format of the input stream to there by produce an output stream corresponding to a digital moving picture under different compression condition, in which the output stream is produced by utilizing added information corresponding to information other than a decoded pixel value of the input stream.
Also, the video coding method is featured by that when the input stream and the output stream own coding modes corresponding to information as to coding methods every subpicture, the coding mode of the output stream is determined based upon a coding mode of the corresponding subpicture of the input stream.
Also, the video coding method is featured by that when the output stream owns a coding mode every picture, the coding mode of the output stream is determined based upon the coding mode of the subpicture contained in the corresponding picture of the input stream.
Also, the video coding method is featured by that the video coding method includes a method for producing/referring to coding mode history information containing information for indicating how many subpictures of the output stream have been continuously inter-coded in the past for plural pictures counted from a picture under being coded; and when a subpicture which is intra-coded while the output stream is compressed is selected from a plurality of subpictures inter-coded in the input stream, the coding mode history information is utilized.
Also, the video coding method is featured by that when both the input stream and the output stream are compressed in the unit of a subpicture by way of a motion-compensatable format, a format of a motion vector of the input stream is changed into a format usable as a motion vector of the output stream, and the format-changed motion vector of the input stream is used as the motion vector of the output stream.
Also, the video coding method is featured by that a starting point for a searching operation is determined based upon a value of a motion vector of an input stream; and a motion vector searching operation is carried out so as to determine a motion vector of an output stream.
Also, the video coding method is featured by that when the motion vector of the input stream is such a motion vector obtained by using a filtering-processed reference image, the motion vector of the output stream is produced by converting the motion vector into a representation obtained by using a reference image to which the filtering process is not performed, and further by converting the converted motion vector into another representation which is obtained by using another filtering-processed reference image different from the reference image of the input stream.
Also, the video coding method is featured by that when the input stream owns both a motion vector every subpicture and subtraction information corresponding to a motion prediction error, a magnitude of the subtraction information is obtained so as to calculate an accurate degree of the motion vector, and a method for utilizing the motion vector of the input stream is changed in response to the magnitude of the accurate degree of the motion vector.
Also, the video coding method is featured by that a search range of a motion vector searching process operation is changed in response to the magnitude of the accurate degree of the motion vector.
Also, the video coding method is featured by that in response to the magnitude of the accurate degree of the motion vector, a judgement is made as to whether or not the motion vector searching process operation is carried out.
Also, the video coding method is featured by that in response to the magnitude of the accurate degree of the motion vector, a method for coding the corresponding subpicture of the output stream is changed.
Also, the video coding method is featured by that an intra picture in which an entire 1 picture is intra-coded is first detected by a video coding method for producing an output stream in the unit of a subpicture before an entire 1 picture of an input stream is entered.
Also, the video coding method is featured by that the intra picture is detected by executing a compression format converting process operation in the unit of the subpicture while producing intra block information corresponding to such information for recording thereon as to whether or not each of the subpictures in the picture of the input stream under process operation is intra-coded so as to detect the intra picture, and also by detecting that all of the subpictures contained in-the picture under process operation are intra-coded by referring to said intra block information at a time instant when all of the subpictures contained in 1 picture are entered from the input stream.
Also, the video coding method is featured by comprising a method for containing a quadrature converting coefficient contained in the input stream, while not inverse-quadrature-converting the input stream into the output stream.
Also, the video coding method is featured by comprising a method for containing a quantized quadrature converting coefficient contained in the input stream, while not inverse-quadrature-converting and not dequantizing the input stream into the output stream.
Also, the video coding method is featured by that in the case that the subpicture of the input stream is intra-coded, the subpicture is intra-coded when the output stream is produced; and either the quadrature converting coefficient or the quantized quadrature converting coefficient of the subpicture of the input stream is employed as either a quadrature converting coefficient or a quantized quadrature converting coefficient of the subpicture of the output stream.
Also, the video coding method is featured by that when a subpicture of the input stream is inter-coded in connection with a motion compensation, the subpicture is inter-coded in connection with the motion compensation while the output stream is produced; and either a quadrature converting coefficient or a quantized quadrature converting coefficient, which corresponds to subtraction information of the subpicture of the input stream, is used as either a quadrature converting coefficient or a quantized quadrature converting coefficient, which corresponds to subtraction information of the subpicture of the output stream.
Also, the video coding method is featured by that with respect to a quantizing matrix indicative of a relationship between a position and a quantizing value within an area in the quadrature converting unit of each of the quadrature converting coefficient, the same quantizing matrix as that of each of the subpictures of the input stream is set to the relevant subpicture of the output stream; and each of the quadrature converting coefficients of the output stream is quantized by the same quantizing value as that of the quadrature coefficient at the corresponding position of the input stream.
Also, the video coding method is featured by that the quantizing value of each of the subpictures of the output stream is set in such a manner that a quantizing value with respect to a quadrature converting coefficient of a low frequency area of the subpicture is made identical to a quantizing value with respect to the corresponding quadrature converting coefficient of the input stream.
Also, the video coding method is featured by that in the case that there are plural subpictures of an input stream corresponding to a subpicture of an output stream, the coding mode of the subpicture of the output stream is set as an intra-coding mode subject when at least one of the subpictures of the corresponding input stream is intra-coded; and the coding mode of the subpicture of the output stream is set to an intra-coding mode in such a case that a total number at which after the subpicture corresponding to the intra-coding mode subject has been finally intra-coded, the subpicture is continuously intra-coded exceeds a predetermined threshold value.
Also, the video coding method is featured by that in the case that a coding order of subpictures contained in 1 picture of an input stream is different from that of an output stream, the output stream is produced after the plural subpictures of the input stream have been stored, the total number being equal to such a number at which the subpictures of the input streams can be continuously coded in the coding order of the output stream.